Single-site catalysts for olefin polymerization

ABSTRACT

A method for making single-site catalysts useful for olefin polymerization is disclosed. A nitrogen-functional heterocycle is first deprotonated with an alkyllithium compound, followed by reaction of this anionic ligand precursor with about 0.5 equivalents of a Group 4 transition metal tetrahalide in a hydrocarbon solvent at a temperature greater than about 10° C. to give an organometallic complex-containing mixture. When combined with exceptionally low levels of an activator (e.g., methyl alumoxane), the mixture actively polymerizes olefins to give polymers with a favorable balance of physical properties, including low density and narrow molecular weight distribution.

FIELD OF THE INVENTION

The invention relates to catalysts useful for olefin polymerization. Inparticular, the invention relates to an improved method for preparing“single-site” catalysts based on heterocyclic ligands such as carbazolyland quinolinoxy ligands.

BACKGROUND OF THE INVENTION

While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture,single-site (metallocene and non-metallocene) catalysts represent theindustry's future. These catalysts are often more reactive thanZiegler-Natta catalysts, and they produce polymers with improvedphysical properties. The improved properties include narrow molecularweight distribution, reduced low molecular weight extractables, enhancedincorporation of α-olefin comonomers, lower polymer density, controlledcontent and distribution of long-chain branching, and modified meltrheology and relaxation characteristics.

Metallocenes commonly include one or more cyclopentadienyl groups, butmany other ligands have been used. Putting substituents on thecyclopentadienyl ring, for example, changes the geometry and electroniccharacter of the active site. Thus, a catalyst structure can befine-tuned to give polymers with desirable properties. “Constrainedgeometry” or “open architecture” catalysts have been described (see,e.g., U.S. Pat. No. 5,624,878). Bridging ligands in these catalysts lockin a single, well-defined active site for olefin complexation and chaingrowth.

Other known single-site catalysts replace cyclopentadienyl groups withone or more heteroatomic ring ligands such as boraaryl (see, e.g., U.S.Pat. No. 5,554,775 or azaborolinyl groups (U.S. Pat. No. 5,902,866).

U.S. Pat. No. 5,539,124 (hereinafter “the '124 patent”) and U.S. Pat.No. 5,637,660 teach the use of anionic, nitrogen-functional heterocyclicgroups such as indolyl, carbazolyl, 2-pyridinoxy or 8-quinolinoxy asligands for single-site catalysts. These ligands, which are produced bysimple deprotonation of inexpensive and readily available precursors,are easily incorporated into a wide variety of transition metalcomplexes. When used with common activators such as alumoxanes, thesecatalysts polymerize olefins to give products with narrow molecularweight distributions that are characteristic of single-site catalysis.

One drawback of the catalysts described above is their relatively lowactivity. Normally, a large proportion of an alumoxane activator must beused to give even a low-activity catalyst system. For example, in the'124 patent, Example 16, a bis(carbazolyl)zirconium complex is used incombination with methylalumoxane at an aluminum:zirconium mole ratio[Al:Zr] of 8890 to 1 to give a catalyst having a marginally satisfactoryactivity of 134 kg polymer produced per gram Zr per hour. In Example 22,a similar complex is used with less activator (i.e., [Al:Zr/h]=1956to 1) to give a catalyst with an activity of only 10 kg/g Zr/h. Theactivator is expensive, and when it is used at such high levels, itrepresents a large proportion of the cost of the catalyst system.Ideally, much less activator would be needed to give a catalyst systemwith better activity.

Another drawback relates to polymer properties. While the '124 patentteaches that catalysts made by its method give polymers with “a narrowmolecular weight distribution,” the actual molecular weightdistributions of polymers made with the bis(carbazolyl)zirconiumdichloride catalysts of Examples 16 and 22 of this reference are notreported. In fact, the molecular weight distributions of these polymerswould preferably be narrower. I found that the MWDs of polymers madeusing the '124 catalysts are actually greater than 3 (see ComparativeExamples 6-8 and 11-13, below).

In sum, there is a continuing need for single-site catalysts that can beprepared inexpensively and in short order from easy-to-handle startingmaterials and reagents. In particular, there is a need for catalyststhat have good activities even at low activator levels. Ideally, thecatalysts would produce, at low activator levels, polyolefins withdesirable physical properties such as good comonomer incorporation,favorable melt-flow characteristics, and narrow molecular weightdistributions.

SUMMARY OF THE INVENTION

The invention is a method for making single-site catalysts useful forolefin polymerization. The method comprises two steps. First, anitrogen-functional heterocycle is deprotonated with an alkyllithiumcompound to produce an anionic ligand precursor. The heterocycle is anindole, carbazole, 8-quinolinol, 2-pyridinol, or a mixture thereof. Inthe second step, the anionic ligand precursor reacts with about 0.5equivalents of a Group 4 transition metal tetrahalide (or with about 1equivalent of an indenyl Group 4 transition metal trihalide) in ahydrocarbon solvent at a temperature greater than about 10° C. to give amixture that contains the desired organometallic complex.

Catalyst systems comprising the organometallic complex-containingmixtures and an activator, as well as olefin polymerization processesthat use the catalyst systems, are also included.

The complex-containing mixture actively polymerizes olefins, even whenused with an exceptionally low level of an activator. Solvent dilutionfurther enhances catalyst activity. In addition, the resulting polymershave a favorable balance of physical properties, including narrow MWD.The method provides a simple route to a variety of heterocycle-based,single-site catalysts and reduces the overall cost of these systems byreducing the amount of costly activator needed for high activity.

DETAILED DESCRIPTION OF THE INVENTION

Catalyst systems prepared by the method of the invention comprise anactivator and an organometallic complex-containing mixture. Thecatalysts are “single site” in nature, i.e., they are distinct chemicalspecies rather than mixtures of different species. They typically givepolyolefins with characteristically narrow molecular weightdistributions (Mw/Mn<3) and good, uniform comonomer incorporation.

The organometallic complex-containing mixture includes a complex thatcontains a Group 4 transition metal, M, i.e., titanium, zirconium, orhafnium. Preferred complexes include titanium or zirconium. The mixturealso normally includes unreacted starting materials and lithium halides.

In one aspect, the invention is a method for preparing theorganometallic complex-containing mixture. The method comprises twosteps: deprotonation of the ligand, and reaction of the anionic ligandprecursor with a Group 4 transition metal tetrahalide.

In the first step, a nitrogen-functional heterocycle is deprotonatedwith an alkyllithium compound. Suitable nitrogen-functional heterocyclesare indoles, carbazoles, 8-quinolinols, and 2-pyridinols. Thesecompounds can have substituents that do not interfere with deprotonationor the subsequent reaction with the transition metal halide. Many ofthese compounds are commercially available or are easily synthesized.For example, indole, carbazole, 8-quinolinol, and 2-pyridinol are allinexpensive and commercially available, and many indoles are easily madefrom arylhydrazones of aldehydes or ketones and a Lewis acid using thewell-known Fischer indole synthesis (see J. March, Advanced OrganicChemistry, 2d ed. (1977), pp. 1054-1055, and references cited therein).Additional examples of suitable nitrogen-functional heterocycles aredescribed in U.S. Pat. Nos. 5,637,660 and 5,539,124, the teachings ofwhich are incorporated herein by reference.

An alkyllithium compound is used to deprotonate the nitrogen-functionalheterocycle. Suitable alkyllithium compounds can be made by reactinglithium with an alkyl halide. More often, they are purchased assolutions in a hydrocarbon (e.g., toluene or hexanes) or ether (e.g.,diethyl ether or tetrahydrofuran) solvent. Preferred alkyllithiumcompounds are C₁-C₈ alkyllithiums such as methyllithium,isopropyllithium, n-butyllithium, or t-butyllithium. n-Butyllithium isparticularly preferred because it is readily available, relatively easyto handle, and effective.

Usually, equimolar amounts of the alkyllithium compound and thenitrogen-functional heterocycle are used to produce the anionicprecursor. Deprotonation can be performed at any suitable temperature,preferably at or below room temperature. While the deprotonationreaction can be performed at temperatures as low as −78° C. or below, itis preferred to perform this step at room temperature. Vigorous mixingis essential because the lithium salt of the anionic ligand tends toprecipitate and forms a thick slurry. The reaction is usually completewithin an hour or two. The resulting anionic ligand precursor includes acarbazolyl, indolyl, 8-quinolinoxy, or 2-pyridinoxy anion and a lithiumcation.

In the second step, the anionic ligand precursor reacts with a Group 4transition metal tetrahalide. Suitable Group 4 transition metaltetrahalides include zirconium, titanium, or hafnium, and four halidegroups, which may the the same or different. Suitable tetrahalidesinclude, for example, zirconium tetrachloride, dibromozirconiumdichloride, titanium tetrabromide, zirconium tetraiodide, hafniumtetrachloride, and the like, and mixtures thereof. Zirconiumtetrachloride and titanium tetrachloride are preferred.

Reaction of about 0.5 equivalents of the Group 4 transition metaltetrahalide with one equivalent of the anionic ligand precursor gives anorganometallic complex-containing mixture that includes the desiredbis(carbazolyl), bis(indolyl), bis(2-pyridinoxy) or bis(8-quinolinoxy)complex. The reaction is performed at temperature greater than about 10°C., which is not only convenient, but gives the best results.Preferably, the reaction occurs at a temperature within the range ofabout 15° C. to about 60° C.; most preferably, the reaction is simplyperformed at room temperature. The reaction is usually complete within afew hours, but it is often convenient and desirable to allow thereaction to proceed overnight (about 16-18 hours) at room temperature.

The preparation of the organometallic complex-containing mixture isperformed in the presence of a hydrocarbon solvent. Preferredhydrocarbons are aromatic, aliphatic, and cycloaliphatic hydrocarbonshaving from 4 to 30 carbons, preferably 4 to 12 carbons, because theseare conveniently removed from the mixture. Examples include pentanes,hexanes, cyclohexane, octanes, toluene, xylenes, and the like, andmixtures thereof.

When the reaction is complete, the mixture is preferably justconcentrated by solvent removal under a stream of nitrogen or withvacuum stripping to give a solid residue that contains the desiredorganometallic complex in addition to some unreacted starting materialsand some lithium halide salt as a by-product. This mixture commonlycontains as much as 50 wt. % of recovered starting material (e.g.,carbazole). Nonetheless, this residue is well-suited for use “as is” ina subsequent olefin polymerization. Also suitable, although lessdesirable, is to filter a solution of the organometalliccomplex-containing mixture to remove insoluble by-products.

Preferred organometallic complexes have the general structure LL′MX₂,wherein M is zirconium or titanium, X is a halogen, and each of L andL′, which may be the same or different, is selected from the groupconsisting of indolyl, carbazolyl, 8-quinolinoxy, and 2-pyridinoxy. Morepreferably, X is Cl or Br.

In a second method of the invention, the anionic ligand precursor isinstead reacted with about one equivalent of an indenyl Group 4transition metal trihalide under the conditions described above. Theindenyl Group 4 transition metal trihalide is conveniently madeaccording to well-known methods by reacting an indenyl anion with aGroup 4 transition metal tetrahalide. The indenyl anion is produced bydeprotonating indene with a potent base such as an alkyllithium compoundor a Grignard reagent. Examples 28-30 below illustrate the secondmethod.

Organometallic complex-containing mixtures of the invention are normallycombined with an activator when they are used to polymerize olefins. Asillustrated below in Example 2, the activator is commonly mixed with thecomplex just prior to use as a catalyst.

Suitable activators are well known in the art. Examples includealumoxanes (methyl alumoxane (MAO or PMAO), modified methyl alumoxane(MMAO), ethyl alumoxane, diisobutyl alumoxane), alkylaluminum compounds(triethylaluminum, diethyl aluminum chloride, trimethylaluminum,triisobutyl aluminum), and the like. Suitable activators include acidsalts that contain non-nucleophilic anions. These compounds generallyconsist of bulky ligands attached to boron or aluminum. Examples includelithium tetrakis(penta-fluorophenyl)borate, lithiumtetrakis(pentafluorophenyl)aluminate, aniliniumtetrakis(pentafluorophenyl)borate, and the like. Suitable activatorsalso include organoboranes, which include boron and one or more alkyl,aryl, or aralkyl groups. Suitable activators include substituted andunsubstituted trialkyl and triarylboranes such astris(pentafluorophenyl)borane, triphenylborane, tri-n-octylborane, andthe like. These and other suitable boron-containing activators aredescribed in U.S. Pat. Nos. 5,153,157, 5,198,401, and 5,241,025, theteachings of which are incorporated herein by reference. Alumoxanes areparticularly preferred activators; methyl alumoxane is most preferred.

The amount of activator needed relative to the amount of organometalliccomplex depends on many factors, including the nature of the complex andactivator, the desired reaction rate, the kind of polyolefin product,the reaction conditions, and other factors. Generally, however, when theactivator is an alumoxane or an alkyl aluminum compound, the amount usedwill be within the range of about 0.01 to about 500 moles, preferablyfrom about 0.1 to about 300 moles, of aluminum per mole of M. When MAOis used, it is preferably used at a [Al:M] molar ratio of less thanabout 500, more preferably less than about 300. When the activator is anorganoborane or an ionic borate or aluminate, the amount used will bewithin the range of about 0.01 to about 5000 moles, preferably fromabout 0.1 to about 500 moles, of activator per mole of M.

The ability to use low levels of an activator is a key advantage of theinvention. As the examples below illustrate, MAO can be used at muchlower levels than previously employed. While MAO is commonly used at[AI:M] molar ratios in the thousands (see U.S. Pat. No. 5,539,124 atExamples 16 and 22), I have now found that molar ratios as low as[Al:M]=200 or below can give catalysts with excellent activity when thecomplex is prepared as described herein. This is a valuable discoverybecause the activator is a major contributor to overall catalyst cost,and ways to reduce its use have long been sought by the industry.

Storage stability is another advantage of catalyst systems prepared bythe method of the invention. As the results in Table 2 below confirm,aging has a dramatic negative effect on the activity of the catalystsmade using the methods described in the '124 patent. In contrast,catalysts made by the method of the invention retain excellent activity,and polymers made using the catalysts of the invention have consistentlynarrow MWDs, even after 75 hours of storage.

If desired, a catalyst support such as silica or alumina can be used.However, the use of a support is generally not necessary for practicingthe process of the invention.

Catalysts made by the method of the invention are particularly valuablefor polymerizing olefins. Preferred olefins are ethylene and C₃-C₂₀α-olefins such as propylene, 1-butene, 1-hexene, 1-octene, and the like.Mixtures of olefins can be used. Ethylene and mixtures of ethylene withC₃-C₁₀ α-olefins are especially preferred.

Many types of olefin polymerization processes can be used. Preferably,the process is practiced in the liquid phase, which can include slurry,solution, suspension, or bulk processes, or a combination of these.High-pressure fluid phase or gas phase techniques can also be used. Theprocess of the invention is particularly valuable for solution andslurry processes.

The olefin polymerizations can be performed over a wide temperaturerange, such as about −30° C. to about 280° C. A more preferred range isfrom about 30° C. to about 180° C.; most preferred is the range fromabout 60° C. to about 100° C. Olefin partial pressures normally rangefrom about 15 psig to about 50,000 psig. More preferred is the rangefrom about 15 psig to about 1000 psig.

Catalyst concentrations used for the olefin polymerization depend onmany factors. Preferably, however, the concentration ranges from about0.01 micromoles per liter to about 100 micromoles per liter.Polymerization times depend on the type of process, the catalystconcentration, and other factors. Generally, polymerizations arecomplete within several seconds to several hours.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

EXAMPLE 1 Preparation of Bis(carbazolyl) Zirconium Dichloride

Carbazole (5.0 g, 30 mmol) is stirred in a flask under an atmosphere ofnitrogen in a dry box for 15 min. Toluene (120 mL) is added, and themixture is stirred for 30 min. n-Butyllithium (12 mL of 2.5 M solutionin hexane, 30 mmol) is added by syringe over 5 min. to the stirredcarbazole solution. The mixture is stirred at room temperature for 2 h.The mixture turns light pink, and the slurry becomes thick, requiringvigorous stirring. Zirconium tetrachloride (3.50 g, 15 mmol) and moretoluene (25 mL) are added to the flask, and the mixture turns brown.Stirring is continued at room temperature for another 18 h, after whichthe mixture is black-brown-green. Solvents are removed under a flow ofnitrogen, and the residue is vacuum dried for 3 h. A yellow solid (9.25g), which contains the desired bis(carbazolyl) complex (about 36 wt. %)along with unreacted starting materials (about 50 wt. %) and somelithium chloride (about 3 wt. %) is isolated.

EXAMPLE 2 Ethylene Polymerization

A portion of the bis(carbazolyl) zirconium dichloride-containing mixtureprepared in Example 1 (0.10 g) is dissolved in toluene (20 mL) in asmall bottle and is stirred under nitrogen at room temperature for 30min. The mixture has a concentration of bis(carbazolyl)zirconiumdichloride in the solution of 0.0018 g/cm³ (0.0036 mmol/cm³). A sampleof this mixture (0.5 mL) is used as the catalyst solution in thereaction described below. Ethylene, isobutane, and nitrogen are driedprior to use with 13X molecular sieves.

A 2-L stainless-steel reactor is preconditioned by heating it to 120° C.and maintaining that temperature for 20 min. under a flow of nitrogen.

Triisobutylaluminum (0.5 mL or 3.0 mL of a 0.9 M solution in heptane,0.45 or 2.7 mmol; the amount used depends upon the moisture level of thefeedstock and the reactor system) is charged to one side of a two-sideinjector. The other side of the injector is charged with the catalystsolution (0.5 mL), toluene (0 mL in this example), and methylaluminoxane(10% MAO in toluene, 2.18 M solution, product of Akzo Nobel, 0.165 mL,molar ratio of [Al:Zr]=200).

1-Hexene (100 mL) is added to the reactor first. The triisobutylaluminumsolution is then flushed into the reactor with isobutane (750 mL). Theagitator is started, and the temperature controller is set to maintain aconstant reactor temperature of 75° C.

The reactor is pressurized with ethylene to 400 psig. Thecatalyst/activator mixture is injected into the reactor along with moreisobutane (50 mL) to initiate the polymerization. Ethylene is fed ondemand using a Brooks mass flow meter to maintain a pressure of 400 psigin the reactor. The concentration of ethylene in the isobutane is about13 mole %. The polymerization continues at 75° C. for 0.5 to 1 hour, andis then terminated by closing the ethylene feed valve and venting thereactor. The resulting polyethylene is collected and dried under vacuumat 50° C.

Catalyst activity: 150 kg/g Zr/h. Polymer properties: melt index:

0.11 dg/min.; MIR: 19; Mw/Mn: 2.49; density: 0.921 g/cm³.

EXAMPLE 3 Ethylene Polymerization: Effect of Diluting Catalyst Solution

The procedure of Example 2 is followed, but the catalyst solution (0.5mL) is diluted with 1.0 mL of toluene prior to adding it to theinjector.

Catalyst activity: 310 kg/g Zr/h. Polymer properties: melt index: 0.12dg/min.; MIR: 19; Mw/Mn: 2.52; density: 0.919 g/cm³.

EXAMPLE 4 Ethylene Polymerization: Effect of Further Dilution

The procedure of Example 2 is followed, except that the catalystsolution has an intial concentration of 0.0009 g/cm³ ofbis(carbazolyl)zirconium dichloride (instead of 0.0018 g/cm³) and 1.0 mLof this solution is added (rather than 0.5 mL), along with 1.0 mL oftoluene, to the injector.

Catalyst activity: 460 kg/g Zr/h. Polymer properties: melt index: 0.14dg/min.; MIR: 18; Mw/Mn: 2.45; density: 0.918 g/cm³.

Comparative Example 5 Preparation of a Bis(carbazolyl) Zirconium Complex

The procedure of Example 16 of U.S. Pat. No. 5,539,124 is followed toprepare a bis(carbazolyl) zirconium complex. This procedure usesmethylmagnesium bromide to deprotonate carbazole, and combines theresulting anion with 0.5 eq. of zirconium tetrachloride in ether at −78°C. After warming to room temperature, the mixture is stripped to removeether. Toluene is added, and the mixture is filtered to remove insolublematerial. The filtrate is then stripped to yield the bis(carbazolyl)complex.

Comparative Example 6 Ethylene Polymerization

The procedure of Example 2 is followed, except that the bis(carbazolyl)zirconium complex prepared in Comparative Example 5 is used.

Catalyst activity: 18 kg/g Zr/h. Polymer properties: melt index: 0.08dg/min.; MIR: 25; Mw/Mn: 3.12; density: 0.925 g/cm³.

Comparative Example 7 Effect of Dilution

The procedure of Example 3 is followed, except that the bis(carbazolyl)zirconium complex prepared in Comparative Example 5 is used.

Catalyst activity: 30 kg/g Zr/h. Polymer properties: melt index: 0.09dg/min.; MIR: 25; Mw/Mn: 3.14.

Comparative Example 8 Effect of Further Dilution

The procedure of Example 4 is followed, except that the bis(carbazolyl)zirconium complex prepared in Comparative Example 5 is used.

Catalyst activity: 35 kg/g Zr/h. Polymer properties: melt index: 0.09dg/min.; MIR: 25; Mw/Mn: 3.22.

Comparative Example 9 Ethylene Polymerization: Increased MAO Level

The data reported in Table 1 below for this example are obtained orcalculated from Example 16 of U.S. Pat. No. 5,539,124, and are usedherein as a comparison. Molar ratio of [Al/Zr]=8890; Catalyst activity:134 kg/g Zr/h.

Comparative Example 10 Preparation of a Bis(carbazolyl) ZirconiumComplex

The procedure of Example 22 of U.S. Pat. No. 5,539,124 is followed toprepare bis(carbazolyl) zirconium dichloride. This procedure reactstetrakis(diethylamido)zirconium with carbazole followed by chlorinationwith silicon tetrachloride.

Comparative Example 11 Ethylene Polymerization

The procedure of Example 2 is used, except that the bis(carbazolyl)zirconium complex prepared in Comparative Example 10 is used.

Catalyst activity: 12 kg/g Zr/h. Polymer properties: melt index: 0.05dg/min.; MIR: 29; Mw/Mn: 3.15.

Comparative Example 12 Effect of Dilution

The procedure of Example 3 is used, except that the bis(carbazolyl)zirconium complex prepared in Comparative Example 10 is used.

Catalyst activity: 20 kg/g Zr/h. Polymer properties: melt index: 0.06dg/min.; MIR: 29; Mw/Mn: 3.21; density: 0.925 g/cm³.

Comparative Example 13 Effect of Further Dilution

The procedure of Example 4 is used, except that the bis(carbazolyl)zirconium complex prepared in Comparative Example 10 is used.

Catalyst activity: 24 kg/g Zr/h. Polymer properties: melt index: 0.07dg/min.; MIR: 30; Mw/Mn: 3.32; density: 0.925 g/cm³.

Comparative Example 14 Ethylene Polymerization: Increased MAO Level

The data reported in Table 1 below for this example are obtained orcalculated from Example 22 of U.S. Pat. No. 5,539,124, and are usedherein as a comparison. Molar ratio of [Al/Zr]=1956; Catalyst activity:10 kg/g Zr/h.

Comparative Example 15 Ethylene Polymerization using a MetalloceneComplex

The procedure of Example 2 is followed, except that complex used isbis(n-butylcyclopentadienyl)zirconium dichloride, which is aconventional metallocene complex.

Catalyst activity: 147 kg/g Zr/h. Polymer properties: melt index: 0.11dg/min.; MIR: 20; Mw/Mn: 2.82; density: 0.922 g/cm³.

Comparative Example 16 Metallocene Complex: Effect of Dilution

The procedure of Example 3 is followed, except thatbis(n-butyl-cyclopentadienyl)zirconium dichloride is used as thecomplex.

Catalyst activity: 230 kg/g Zr/h. Polymer properties: melt index: 0.11dg/min.; MIR: 23; Mw/Mn: 2.76; density: 0.922 g/cm³.

Comparative Example 17 Metallocene Complex: Effect of Further Dilution

The procedure of Example 4 is followed, except thatbis(n-butyl-cyclopentadienyl)zirconium dichloride is used as thecomplex.

Catalyst activity: 240 kg/g Zr/h. Polymer properties: melt index: 0.12dg/min.; MIR: 21; Mw/Mn: 2.74; density: 0.921 g/cm³.

EXAMPLES 18 AND 19 Reproducible Catalyst Preparation

The procedure of Example 3 is repeated twice. The activity and polymerproperty results demonstrate the reproducibility of the catalystpreparation method:

Example 18: Catalyst activity: 305 kg/g Zr/h. Polymer properties: meltindex: 0.11 dg/min.; MIR: 19; Mw/Mn: 2.44; density: 0.920 g/cm³.

Example 19: Catalyst activity: 316 kg/g Zr/h. Polymer properties: meltindex: 0.12 dg/min.; MIR: 19; Mw/Mn: 2.38; density: 0.919 g/cm³.

Table 1 summarizes all of the results from the preceding examples. Asthe table shows, catalysts made by the method of the invention are muchmore active than bis(carbazolyl)zirconium complexes prepared asdescribed in U.S. Pat. No. 5,539,124. In particular, the amount of MAOactivator required for high activity is greatly reduced from a molarratio [Al:Zr] of thousands to [AI:Zr] =200 (compare Example 2 withComparative Examples 6 and 9). This is valuable because the activator isnormally a major contributor to the cost of the catalyst system, andways to reduce the amount needed are coveted by the industry.

Table 1 also illustrates the strong activating effect of solvents forcatalyst systems of the invention. While the trend is the same in theprior-art catalysts, diluting catalysts of the invention increasesactivity threefold (see Examples 2-4) versus twofold for earlierbis(carbazolyl)zirconium catalysts (Comparative Examples 6-8 and 11-13).A weaker activating effect of dilution is also observed with aconventional metallocene, bis(n-butylcyclopentadienyl)zirconiumdichloride (Comparative Examples 15-17).

In sum, when MAO is used as an activator at a molar ratio of[Al:Zr]=200, the catalyst systems of the invention are as active as thebenchmark metallocene, bis(n-butylcyclopentadienyl)zirconium dichloride,and they are much more active than earlier bis(carbazolyl)zirconiumcomplexes.

Table 1 also summarizes polymer properties. Polyethylene made using thecatalyst systems has a favorable balance of properties, including goodmelt index and MIR, and narrow molecular weight distribution. In fact,the Mw/Mn values of polymers made using the catalyst systems of theinvention, typically 2.4-2.5, are much narrower than those made fromearlier bis(carbazolyl)zirconium complexes (3.1-3.3), and they aresomewhat narrower than those of polymers made usingbis(n-butylcyclopentadienyl)zirconium dichloride (2.7-2.8). Lowdensities are also easily achieved, which indicates that the 1-hexenecomonomer is efficiently incorporated into the polymer.

Example 20 and Comparative Examples 21-23 Effect of Aging on CatalystActivity and Polymer Properties

The impact of aging on catalyst activity and polymer properties isevaluated as follows. A bis(carbazolyl)zirconium catalyst of theinvention (prepared in Example 1) is compared withbis(n-butylcyclopentadienyl)-zirconium dichloride and the catalystsprepared in Comparative Examples 5 and 10. A series of ethylenepolymerizations is performed using the procedure of Example 3. Each ofthe four catalysts is aged in a dry box under nitrogen at roomtemperature for 1, 5, 10, 20, 30, 60, and 75 days prior to use in anethylene polymerization. Table 2 summarizes the observed catalystactivities and polymer molecular weight distributions (Mw/Mn).

As the results in Table 2 indicate, aging has a dramatic negative effecton the activity of the catalysts made in Comparative Examples 5 and 10,which are made using procedures from U.S. Pat. No. 5,539,124. Thesecatalysts would not polymerize ethylene at all with an activator (MAO)level of [Al:Zr] molar ratio=200 if the catalyst had been aged for 10days or more. The results for Comparative Examples 21 and 22 areconsistent with teachings in the '124 patent, which advises a skilledperson to use this catalyst “as promptly as possible as it may lose someactivity during storage.”

In contrast, when a catalyst made by the method of the invention is used(Example 20), the catalyst retains excellent activity, even after 75days of storage; no measurable amount of activity loss is observed. Themetallocene control (Comparative Example 23) also retains its highactivity after prolonged storage.

Also interesting is the impact of storage on polymer molecular weightdistribution. Comparative Examples 21 and 22 show considerablebroadening of molecular weight distribution over a few samples. On theother hand, the catalyst of the invention gives polymers with aconsistently narrow Mw/Mn, even after 75 hours of storage; themetallocene control gives polymers with slightly broader Mw/Mn values,but ones that are also not very sensitive to aging.

EXAMPLES 24-30 Versatility of the Catalyst Preparation Method

The procedure of Example 1 is generally followed to make the 15bis(carbazolyl), bis(8-quinolinoxy), and bis(indolyl) zirconium ortitanium complexes listed in Table 3 (Examples 24-27) from zirconiumtetrachloride or titanium tetrachloride. The starting materials formaking the ligands are carbazole, 8-quinolinol, and indole. Eachcatalyst is used to polymerize ethylene using the process of Example 3.The results from these polymerizations appear in Table 3.

A similar method is used to make the indenylzirconium complexes(Examples 28-30), except that indenylzirconium trichloride is firstprepared, followed by reaction with one equivalent of the anionic ligandprecursor, which is made by deprotonating indole, carbazole, or8-quinolinol with one equivalent of n-butyllithium. Each catalyst isused to polymerize ethylene using the process of Example 3. The resultsfrom these polymerizations appear in Table 3.

As shown in the table, the method of the invention is valuable forpreparing a wide variety of complexes based on nitrogen-functionalheterocyclic ligands. With a low level of MAO activator ([Al:M] molarratio =200), each catalyst has good activity and incorporates 1-hexenewell to produce low-density polymers.

The preceding examples are meant only as illustrations. The followingclaims define the invention.

TABLE 1 Ethylene Polymerization Results Ex. MAO [Al:Zr] Conc. AddedToluene Activity MI Density # Catalyst Source molar ratio (g/mL) (mL)(mL) (kg/g Zr/hr) (dg/min) MIR MWD (g/mL) 2 bis(carbazolyl) Zr Ex. 1 200 0.0018 0.5 0 150  0.11 19 2.49 0.921 3 complex 200 0.0018 0.5 1 310 0.12 19 2.52 0.919 4 200 0.0009 1.0 1 460  0.14 18 2.45 0.918 C6bis(carbazolyl) Zr Comp. 200 0.0018 0.5 0 18 0.08 25 3.12 0.925 C7complex Ex. 5  200 0.0018 0.5 1 30 0.09 25 3.14 — C8 200 0.0009 1.0 1 350.09 25 3.22 — C9 8890*  — — — 134* — — — — C11 bis(carbazolyl) Zr Comp.200 0.0018 0.5 0 12 0.05 29 3.15 — C12 complex Ex. 10 200 0.0018 0.5 120 0.06 29 3.21 0.925 C13 200 0.0009 1.0 1 24 0.07 30 3.32 0.925 C141956* — — —  10* — — — — C15 bis(n-butylcyclo- 200 0.0018 0.5 0 147 0.11 20 2.82 0.922 C16 pentadienyl) 200 0.0018 0.5 1 230  0.11 23 2.760.922 C17 zirconium dichloride 200 0.0009 1.0 1 240  0.12 21 2.74 0.92118 bis(carbazolyl) Zr Ex. 1  200 0.0018 0.5 1 305  0.11 19 2.44 0.920 19complex 200 0.0018 0.5 1 316  0.12 19 2.38 0.919 *Values obtained orcalculated from U.S. Pat. No. 5,539,124

TABLE 2 Effect of Aging on Catalyst Activity and Polymer MolecularWeight Distribution Days Aged --> Ex. Catalyst Source 1 5 10 20 30 60 75Catalyst Activity (kg/g Zr/h) 20 bis(carbazolyl) Zr complex Ex. 1 310290 297 310 315 300 320 C21 bis(carbazolyl) Zr complex C. Ex. 5  30 12 0— — — — C22 bis(carbazolyl) Zr complex C. Ex. 10 20 8 0 — — — — C23bis(n-BuCp)ZrCl₂ 230 230 240 235 240 235 230 Polymer Mol. Wt.Distribution (Mw/Mn) 20 bis(carbazolyl) Zr complex Ex. 1 2.52 2.49 2.582.42 2.45 2.52 2.44 C21 bis(carbazolyl) Zr complex C. Ex. 5  3.14 3.26 —— — — — C22 bis(carbazolyl) Zr complex C. Ex. 10 3.21 3.32 — — — — — C23bis(n-BuCp)ZrCl₂ 2.82 2.76 2.74 2.78 2.76 2.68 2.72

TABLE 3 Additional Ethylene Polymerization Examples MAO [Al:Zr] Conc.Added Toluene Activity MI Density Ex. # Catalyst molar ratio (g/mL) (mL)(mL) (kg/g M/hr) (dg/min) MIR MWD (g/mL)  3 bis(carbazolyl)ZrCl₂ 2000.0018 0.5 1 310 0.12 19 2.52 0.919 24 bis(carbazolyl)TiCl₂ 200 0.00180.5 1 348 0.03 25 3.45 0.924 25 bis(8-quinolinoxy)ZrCl₂ 200 0.0018 0.5 1230 0.06 24 3.15 0.920 26 bis(8-quinolinoxy)TiCl₂ 200 0.0018 0.5 1 6600.02 24 3.72 0.922 27 bis(indolyl)ZrCl₂ 200 0.0018 0.5 1 208 0.07 263.57 0.918 28 Indolyl(indenyl)ZrCl₂ 200 0.0018 0.5 1 260 0.35 24 4.030.917 29 Carbazolyl(indenyl)ZrCl₂ 200 0.0018 0.5 1 360 0.36 20 2.700.916 30 8-Quinolinoxy(indenyl)ZrCl₂ 200 0.0018 0.5 1 255 0.42 19 3.480.919

I claim:
 1. A method which comprises: (a) deprotonating a compoundselected from the group consisting of indoles, carbazoles,8-quinolinols, 2-pyridinols, and mixtures thereof, with an alkyllithiumcompound to produce an anionic ligand precursor; and (b) reacting theanionic ligand precursor with about 0.5 equivalents of a Group 4transition metal tetrahalide at a temperature greater than about 10° C.in the presence of a hydrocarbon solvent to produce an organometalliccomplex-containing mixture.
 2. The method of claim 1 wherein the ligandprecursor is a carbazolyl anion.
 3. The method of claim 1 wherein thealkyllithium compound is a C₁-C₈ alkyllithium compound.
 4. The method ofclaim 1 wherein the alkyllithium compound is n-butyllithium.
 5. Themethod of claim 1 wherein the Group 4 transition metal tetrahalide isselected from the group consisting of zirconium tetrachloride andtitanium tetrachloride.
 6. The method of claim 1 wherein step (b) isperformed at a temperature within the range of about 15° C. to about 60°C.
 7. The method of claim 1 wherein step (b) is performed at roomtemperature.
 8. The method of claim 1 wherein one component of themixture is an organometallic complex having the structure LL′MCl₂,wherein M is titanium or zirconium, and each of L and L′, which may bethe same or different, is selected from the group consisting of indolyl,carbazolyl, 8-quinolinoxy, and 2-pyridinoxy.
 9. The method of claim 1further comprising concentrating the product from step (b) withoutremoving insoluble products.
 10. An organometallic complex-containingmixture made by the method of claim
 1. 11. An organometalliccomplex-containing mixture made by the method of claim
 9. 12. A catalystsystem which comprises: (a) an activator; and (b) the organometalliccomplex-containing mixture of claim
 10. 13. A catalyst system whichcomprises: (a) an activator; and (b) the organometalliccomplex-containing mixture of claim
 11. 14. A method which comprises:(a) deprotonating a compound selected from the group consisting ofindoles, carbazoles, 8-quinolinols, 2-pyridinols, and mixtures thereof,with an alkyllithium compound to produce an anionic ligand precursor;and (b) reacting the anionic ligand precursor with about 1 equivalent ofan indenyl Group 4 transition metal trihalide at a temperature greaterthan about 10° C. in the presence of a hydrocarbon solvent to produce anorganometallic complex-containing mixture.
 15. The method of claim 14further comprising concentrating the product from step (b) withoutremoving insoluble products.